How do you solve the system of equations x= - 4 and - 8x - 5y = - 18 by using substitution?

1 Answer
Mar 14, 2017

Y is equal to 10. For how, see the explanation.

Explanation:

Substitute x with -4 in the second equation.
This gets you:
-8(-4) - 5y = -18
Multiply -8 and -4:
32 - 5y = -18
Subtract 32 from both sides:
-5y = -50
Divide both sides by negative five:
y = 10
You don't need to find x, since it's already given.
There are other ways to solve this with substitution, involving adding or subtracting different things in a different order, but they all end up with the same answer.